Viral diseases have a significant impact on livestock throughout the world. Porcine reproductive and respiratory syndrome virus (PRRSV) is the causative agent of a disease characterized by respiratory disorders in young pigs and reproductive failure in sows (Benfield et al., 1992, J. Vet. Diagn. Invest., 4:127-133, Collins et. al., 1992, J. Vet. Diagn. Invest., 4:117-126, Wensvoort et al., 1991, Vet. Q., 13:121-130) and is now endemic in most countries. The disease is characterized by reproductive failure in pregnant sows and respiratory problems in pigs of all ages. The disease has a significant economic impact on the swine industry, and in the United States is estimated to result in economic loses of $664 million per year (Holtkamp et al., 2013, J Swine Health Prod., 21(2):72-84).